Characterization of Al_xGa_1-xAs layers grown on (100) GaAs by metallic-arsenic-based-MOCVD

We present the electrical and structural characterization of Al_xGa_1-xAs layers grown in a metallic-arsenic-based-MOCVD system. The gallium and aluminium precursors were the metal-organic compounds trimethylgallium (TMGa) and trimethylaluminium (TMAl), respectively. Al_xGa_1-xAs layers that were grown at temperatures less than 750 °C present a high electrical resistivity. Independent of the used III/V ratio the samples that were grown at temperatures greater that 750 °C were n-type with an electron concentration of around 10¹⁷ cm^-3 and a carrier mobility of 2200 cm²/V-s. Chemical composition studies by SIMS exhibit the presence of silicon, carbon and oxygen as the main residual impurities. Silicon concentration of around of 10¹⁷ cm^-3 is very close to the free carrier concentration determined by the Hall-van der Pauw measurements. Composition homogeneity and structural quality are demonstrated by Raman measurements. As the growth temperature is increased the layers compensation decreases but the Raman spectra show that the crystalline quality of the layers diminishes.